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The Low-Down on Hydrogen Fuel Cells

By Trucktruth.com, May 15th, 2009

When most companies begin to consider alternative power for lift trucks, hydrogen fuel cells are typically the first technology that comes to mind, due in part to well-publicized trial deployments. Hydrogen fuel cells power electric trucks as do batteries, but they are different from batteries in how they operate. The basic operating principle of a proton exchange membrane (PEM) hydrogen fuel cell follows. Two reactants, hydrogen and oxygen, are channeled through grooves along opposite electrodes. An electrolyte separating the two electrodes causes the hydrogen to separate into positive hydrogen ions and negative electrons. The positive hydrogen ions pass through the electrolyte membrane to combine with the oxygen and form water, a by-product, while the negative ions, or electrons, pass through an external circuit to get to the opposite electrode. This flow of electrons creates the electrical current. Unlike a battery, which must be recharged after use, a fuel cell will produce electric current continuously, provided that there is a continuous supply of hydrogen fuel and oxygen. The process is depicted in the image below, taken from the Wikipedia fuel cell page.

Although the technology has been around for a few years, commercialized fuel cells for the lift truck industry remains in its infancy. The level of fit for this technology in the lift truck industry is not yet fully understood, so it is worthwhile to explore the areas of costs, performance, operational factors, and environmental impact with respect to lift trucks.

Cost factors – Costs associated with the use of HFC’s include the purchase costs, maintenance and replacement costs, and the cost of fuel delivery. The initial purchase costs of an HFC may be between two and three times the cost of a single lead acid battery for an application. The cost of the HFC varies with the kW rating. Maintenance costs can be as much as five times that of a lead acid battery. The annual cost of the hydrogen fuel itself may also be around five times that of the equivalent electricity consumed in a battery application.

Hydrogen fuel infrastructure – Hydrogen fuel delivery also involves infrastructure costs, which will include some combination of fuel delivery, pumps, compressors, vaporizers, high-pressure storage, and dispensing stations, depending upon the rate of fuel consumption. These costs tend to be very high and can be rolled into a lease, depending upon the supplier. Before hydrogen can be used in an HFC, it must be compressed to approximately 5000 psi. Fuel can be delivered to the site location in gaseous form already pressurized in tube trailers at around 6000 psi for lower volume applications, or it can be delivered in liquid form via tanker trucks for higher volume applications. The cost for delivery of hydrogen varies with volume and travel distance. If delivered in liquid form, it must be vaporized and pressurized on site. For the highest volume applications, a higher cost higher throughput liquid pump is used to pressurize the hydrogen prior to vaporization. If delivered in gaseous form in a tube trailer, the hydrogen may be further pressured by means of a compressor, and transferred to on-site high pressure tube storage. Once the hydrogen is vaporized and stored at high pressure, it can be transferred to the HFC by means of a specialized hydrogen dispenser, which may have an appearance similar to that of a gasoline pump, or it may be wall-mounted. The basic flow of hydrogen fuel delivery, storage and dispensing are depicted in the image below.

Performance – In regard to performance, the power rating of the HFC must be sufficient to meet the demands of the application. Specifically, the peak power delivery must be adequate to meet surge requirements for hoist operations or travelling up a ramp, which might last five seconds or more in duration. Continuous power capability must be able to meet average current demand for the shift. Within the lift truck industry, applications span a broad range from light duty cycles with little hoisting to heavy duty cycles with intensive hoisting. It is important to characterize the electrical current demand profile in each application to determine what power rating is required in an HFC. Also, in regard to temperature performance, it must be noted that HFC’s are not yet proven to be suitable for applications with temperatures at or below freezing.

Operational factors – The single most striking advantage of the HFC option for lift trucks is that it offers a three minute recharge (refuel) for an emission-free electric truck. This reduces refueling downtime to less than that of an LPG truck. It enables substantial productivity gains, particularly in a three shift scenario, over both battery electric trucks and LPG trucks. Operationally, the short refuel time eliminates the need for battery change operations, including space for inventory, handling equipment, and dedicated personnel. However, battery change operations can be eliminated only for those trucks/applications for which there is a commercially available properly sized HFC pack. For some fleets it may be that there is a fuel cell offering for some but not all truck models within the fleet, particularly if the fleet spans classes I, II and III.

Environmental impact – As described in the overview above, while HFC lift trucks provide for zero emissions at the point of use, making them superior to ICE trucks and equivalent to battery electric trucks, power plant emissions would be on the order of 2.5 time greater than those associated with battery electric trucks. Additionally, unless hydrogen is generated on site, the fuel must be transported around in trucks, further contributing to greenhouse gas emissions. Therefore, converting from ICE-powered trucks to HFC-powered trucks would provide a favorable environmental impact, but converting from battery electric trucks to HFC electric trucks would have an unfavorable overall environmental impact, until hydrogen is produced and transported without emission.

The advantages and disadvantages of HFC-powered electric lift trucks can be summarized as follows:

Advantages
• Zero-emissions at the point of use
• Very fast refueling time
  • Potential for increased productivity
  • Reduced battery inventory
  • Potential to eliminate battery change equipment, space and personnel
• Longer run times possible, depending upon size of fuel storage tank
• Voltage and truck performance remain stable over a shift
• Long-term potential to accommodate the potential use of non-fossil fuel renewable energy
• Less noise and vibration compared to ICE trucks

Disadvantages
• Up-front capital costs, both on-truck and infrastructure costs
• Not yet a commercially mature fuel cell product, with gaps in class and model coverage
• Not yet well-characterized for high intensity applications
• Increased maintenance costs versus a battery
• Higher fuel costs
• Hydrogen fuel delivery is not readily available in all areas, delivery infrastructure is not mature
• Less energy efficient than battery electric
• Fuel cell stack life is not well proven
• Not proven to be suitable for freezer applications.
• Currently produced from fossil fuels in many cases. (Commercial bulk hydrogen is usually produced by the steam reforming of natural gas.)